Acoustic diaphragm and method of construction



Feb. 17, 1959 2,873,813

ous'rrc DIAPHRAGM AND METHOD OF CONSTRUCTION W. W. HAERTHER, JR, ET AL Filed July 27, 1955 'NVENTORSZ N GI WILLIAM W QAERTHER JR MAURlTZ F. NOREN ATT'YS S at s Pat ACOUSTIC DIAPHRAGM AND METHOD OF CONSTRUCTION William W. Haerther, Jr., Geneva, and Mauritz F. Noren, St. Charles, Ill., assignors to Hawley Products Company, St. Charles, 11]., a corporation of Delaware Application July 27, 1955, Serial No. 524,690 9 Claims. Cl. 181-32 This invention relates to acoustic diaphragms and their method of construction, and in particular to a diaphragm having a central non-planiform projecting portion and a peripheral flexible portion constructed from a normally porous flexible material impregnated with a thermosetting resin.

Several qualities or characteristics are desirable in the construction of an acoustic diaphragm. For example, the shape and rigidity of various portions of the diaphragm are known to affect the efliciency and accuracy of sound production and reproduction. Generally, a diaphragm is designed to provide a central portion having a substantially conical or conoidal shape or some other non-planiform projecting shape, the exact shape depending upon the characteristics which are required for a particular use. Since this central portion acts as the vibrating element of the diaphragm, it should be stiff or rigid and also impervious to the passage of air in order to more efliciently transmit imposed vibrations. The central portion should also be thin and lightweight so as to reduce its momentum.

The peripheral portion of the diaphragm acts as a suspension-or support for the central vibrating portion. The flexibility of this peripheral portion determines the resonant frequency of the diaphragm, and this resonant or natural frequency is preferably kept as low as possible. Flexibility can be attained by shaping the peripheral portion in the form of concentric undulations or corrugations as well as by using a comparatively flexible mater al. It is not considered desirable to construct the central portion of the peripheral portion of different materials because of the dificulties which arise; in manufacturing the diaphragm and also because of the distortion caused by the uneven loading of a diaphragm having seams as compared to one having a seamless, integral body. Prior to this invention, however, it has been nec essary to compromise between the rigidity of the central portion and the flexibility of the peripheral portion when constructing a diaphragm from a single homogeneous material into a seamless, integral body.

A moisture-proof diaphragm is advantageous to pre vent poor reproduction which would result from changes in the moisture content of the diaphragm due to changes in the temperature and humidity of the atmosphere.

One object of the present invention is to provide an acoustic diaphragm having a seamIessintegral body constructedfrom a single homogeneous, normally flexible material so as to give a thin, rigid, lightweight, impervious central portion and a porous peripheral flexible supporting portion.

Another object of the invention is to provide an acoustic diaphragm of the desired qualities in which the central portion and peripheral portion can be given any shape suitable for a particular use, the central portion preferably having a non-planiform projecting shape and. the peripheral portion preferably having a corrugated shape. *Still another object'of the invention is to provide an to form an inner connecting flange 5, a corrugated or.

Z ,8 73 ,8 l3 Patented Feb. 17, 1959' acoustic diaphragm which has a low natural frequency and which is moisture-proof. v

A further object of the invention is to provide an acoustic diaphragm constructed of inexpensive and easily fabricated material.

Still another and important object of the invention is to provide a novel and useful method for the construction of an acoustic diaphragm having an impervious central vibratile portion and a porous peripheral flexible supporting portion whereby the manufacture of the diaphragm can be carried out in an exceptionally eflicient and economical manner.

These and other objects, advantages, and functions of theinvention will become more apparent upon consideration of the following description and accompanying drawing in which:

Fig. 1 is a plan view of an acoustic diaphragm illustrating one embodiment of the invention;

Fig. 2 is an enlarged horizontal sectional view of the same taken on line 2--2 of Fig. l; and

Fig. 3 is a horizontal sectional view of a die pressing mold corresponding to the vertical cross section of the diaphragm shown in Fig. 2 and embodying the method for construction of the diaphragm.

In accordance with the invention, an acoustic diaphragm is provided which includes an integral body of normally porous flexible material impregnated with a thermosetting resin, the body being molded and cured in such a manner that the diaphragm will have an impervious central vi bratile portion and a porous peripheral portion. In its preferred form, the central portion 'of the diaphragm is given a non-planiform projecting shape, generally a comcal or conoidal shape. The central portion of a porous flexible material such as cloth or fabric impregnated with a thermosetting resin is shaped and molded by the application of suificient pressure to cause the thermosetting resin to flow, completely filling the opeings between the threads or fibers of the fabric. The resin is also cured by applying heat, thereby providing an impervious, thin and rigid central vibratile portion of the diaphragm. The peripheral portion of the impregnated fabric is merely cured without the application ofpressure so that the thermosetting resin will not flow and the fabric willretain its porous character and a greater degree of flexibility. Preferably, however, a slight amount of pressure s applied to the peripheral portion in order to shape or emboss the impregnated fabric to form corrugations concentric to the central portion of the diaphragm, this pressure in any event being insuflicient to cause the thermosettmg resin to flow.

Referring now to the drawing, wherein similar reference characters designate corresponding parts throughout, one embodiment of the new acoustic diaphragm 1, illustrated in Figs. 1 and 2, has been integrally formed from a piece of cloth or fabric 2 impregnated with a thermosetting resin. Fig. 2 illustrates the completed diaphragm with the excess fabric of Fig. 1 being cut or trimmed away. The central portion a of the diaphragm 1 is divided into an outer section'3 shaped in the form of a spherical segment and a re-entrant inner section 4 also shaped in the form of .a sperical segment. The peripheral portion b of the dia-. phragm 1 is integral with the central portion a and shaped undulatedsection 6 toprovide greater flexib ilityand a relatively flat, outer supporting flange 7.

Theacoustic diaphragm of the invention is integrally formed in a combination molding and embossing die 8 as illustrated by Fig. 3 which molds and shapes a diaphragm corresponding to that shown in Figs. 1 and 2. While the male member 9of the die meets the female member 10 in that part of the die which forms the central portion a of the diaphragm, the male and female members are 3 spaced from each other in that part of the die which shapes the peripheral-portion b of the diaphragm. Thus; the impregnated fabric 2 is placed between the male member 9 and female member 16 which are then pressed together-so that the central portion a is molded and formed in the desired shape, sufiicient pressure being applied, generally from about 50 to 450 p. s. i., to cause the thermosetting resin to flow and fill the spaces between the fibers of the fabric. The pressure is dependent upon the particular resin employed and the amount of resin used in impregnating the fabric. The peripheral portionb of the diaphragm is merely shaped or embossed because of the spaced relationship of the male and female members of the die. A nominal amount of pressure is applied to emboss the fabric into the desired shape. However, suflieient space must be allowed between the male and female members of the die so that in no event will the thermosetting resinbe caused to flow in the peripheral portion [1. Pressure can be applied to the molding and embossing die 8 by means of a conventional compression molding press, preferably of the typeknown as a toggle press.

The diaphragms made in accordance with the invention can vary from rather small sizes, around one to two inches, for microphone equipment, to sizes of twenty inches or more for loudspeakers. The invention is especially useful in making small sized diaphragrns where the height of the vibratile portion does not exceed one-half of the diameter.

In order to curse the thermosetting resin with which the fabric is impregnated, heat can be suppliedto the die by means of an electrically heated plate which can be bolted to the die. Of course, heat can also be supplied by means of a steam heated press platen, commonly used for this purpose. In general, a temperature of from about 285 to 400 F. is used to cure the thermosetting resin, the temperature depending upon the particular resin employed and the time during which heat is applied. Ordinarily, the entire operation of molding, embossing, and curing can he completed in about five to forty seconds.

The fabric with which the diaphragm is constructed is preferably a closely woven cotton material such as muslin, although other fibrous materials are equally advantageous, such as linen, silk and rayon, or even glass fibers woven into a fabric. Excellent results are obtained in the practice of the invention by using a two to three ounce per yard cotton cloth having a count of about 100 x 100 to about 130 X 130 threads per square inch. Various cornbinations of difierent fibrous materials can be incorporated in the fabric. Generally, any woven, knitted, braided, or crocheted fabric is suitable for the purpose of theinvention in which the fibrous material employed will not decompose or liquefy under the temperatures and pressures employed, particularly in the peripheral portion of the diaphragm which must retain its porous character While the diaphragm is preferably constructed of a single layer of a closely woven fabric, it is also possible to form the diaphrgam from multiple layers of fabric material which has been impregnated with a thermosetting resin. A single'layer'of fabric is generally desirable for smaller diaphragms whereas larger diaphragms usually require the thickness of multiple layers of fabric.

The thermosetting resin employed to impregnate the fabric'is preferably a fusible phenol-formaldehyde resin, although other fusible thermosetting resins such as urea and melamine resins are also useful. The resin is pref erably used in the form of a varnish, a suitable solvent being employed to thin the viscosity of the resin to a point suitable for impregnation of a fabric. Resins in this form are readily obtainable; for example, a solution of ten to twenty percent by weight of phenolformaldehyde' dispersed in ethyl alcohol. has been found to be very advantageous in the practice of the invention. Suflicient resin is impregnated into the fabric to form a protective and moisture-proof coating around the individualfibers, but an excess of resin must be avoided in'the peripheral portion of the diaphragm since the porous character of l, i ai I this portion of the fabric can be retained only if the spaces between the individual fibers are left open. The nature of the thermosetting resin is such that the pressures employed in the central portion of the diaphragm will cause the resin to flow, and upon heat curing of the resin, an impervious, thin and rigid centralportion is formed. In the peripheral portion, however, only a nominal pressure is employed to emboss the impregnated fabric and this pressure is not suflicient to cause the resin to flow. The curing of the resin in the peripheral portion results in a moisture-proof coating of the individual fibers, but the cloth or fabric retains its porous and flexible character.

The following example illustrates a preferred method of forming the acoustic diaphragm of the invention:

A closely woven 2.81 ounce to the yard balloon cloth, .095 inch thick and having a count of 118 X 126 threads per square inch, is saturated with a solution of ten to twenty percent by weight of a fusible phenol-formaldeli dc resin (e. g. Monsanto, Resinox 615) dispersed in ethyl alcohol. After draining otf exc'ess'resin, the impregnated fabric, containing about 20% by weight of resin, is placed in a combination molding and embossingdie, such as is shown in Fig. 3, and approximately 100 p. s. i. pressure is applied, the die being heated to a temperature of from 285 to 409 F., for a period of from five to forty seconds. Preferably, the temperature is maintained from about 300 to 350 P. which corresponds to a molding period of from about fifteen to thirty seconds. The higher pressure of the closing dies in the area a causes the resin to flow. In the" area b, the pressure of the dies is insutficient to cause the resin to flow. However, in both areas a and b the temperature is sufiicient to cure the resin to its infusible state.

The completed diaphragm is'then removed from the die and requires no other processing other than the cutting or trimming away of excess fabric. The area a is non-porous and impervious to the passage of air. The area b is porous and permits the passage of air. The diaphragm contains a weight of infusible resin to cloth of approximately 20%. If desired, it is also possible to construct the die so as to cut away the excess fabric simultaneously with the pressure molding and curing operation.

The new and useful acoustic diaphragm constructed in accordance with the invention is especially adaptable for use in intercommunication systems and the like where the diaphragm is used in a dual function as'both microphone and speaker. The invention providesa. diaphragm which isthin, lightweight and moisture-proof, and which has a rigid, impervious central vibrating portion and aflexible, porous peripheral portion resultingin' a low resonant frequency. In addition, the diaphragm can be constructed of relatively inexpensive materials by avery economical and rapid method of fabrication.

The invention is hereby claimed as follows: 7

l. A method for constructing an acoutic diaphragm which comprises impregnating a normally porous flexible material with a fusible thermosetting resin, shaping said impregnated material by molding and curing a central non-planiform projecting portion at a temperature and. pressure sufficient to cause said resin to flow and to cure said resin to its infusible state, and curing the resin on a peripheral flexible portion at a temperature and pressure below that at which the resin will flow.

2. A method for constructing an acoustic diaphragm which comprises impregnating a normally porous flexible material with a fusible thermosettingresin, shaping said impregnated material by molding and curing a central non-planiform projecting portion at a temperature and pressure sufficient to cause said resin to flow and to cure said resin to its infusible state, and simultaneously embossing and curing the resin on a peripheral flexible portion at a temperature and pressure below that at which the resin will flow.

3. A method for constructing an acoustic diaphragm which comprises impregnating a normally porous flexible woven cloth with a fusible phenol-formaldehyde resin, and shaping said impregnated cloth by molding and curing a central non-planiform projecting portion at a temperature of from about 285 to 400 F. and a pressure of from about 50 to 450 p. s. i, said temperature and pressure sufficient to cause the resin to flow and to cure it to its infusible state, and embossing and curring the resin on a peripheral flexible portion at a temperature and pressure below that at which the resin will flow.

4. An acoustic diaphragm comprising an integral body of normally porous fibrous material in the form of a fabric, said body having an impervious central rigid vibratile portion coated With an infusible thermosetting resin to fill the normally open pores of said fabric and a porous peripheral flexible portion in which the individual fibers are thinly coated with a quantity of an infusible thermosetting resin insufiicient to completely fill the normally open pores of said fabric.

5. An acoustic diaphragm as claimed in claim 4 wherein the thermosetting resin is a phenol-formaldehyde resin.

6. An acoustic diaphragm as claimed in claim 4 wherein the central portion is non-planiform.

7. An acoustic diaphragm as claimed in claim 4 wherein the central portion is non-planiform and the peripheral portion is corrugated concentrically to said central portion.

8. An acoustic diaphragm comprising an integral body of normally porous flexible fibrous material in the form of a fabric, said body having an impervious central rigid non-planiform vibratile portion coated with an infusible thermosetting resin which has been impregnated in its fusible state in the individual fibers of said fabric and cured to its infnsible state under conditions of temperature and pressure sufficient to cause the resin to fiow and fill the normally open pores of said fabric, and said body having a porous peripheral undulated flexible portion in which the individual fibers are thinly coated with the same infusible thermosetting resin which has been impregnatecl in its fusible state in the individual fibers of said fabric and cured to its infusible state under conditions of temperature and pressure insuflicient to cause said resin to flow and till the normally open pores of said fabric.

9. An acoustic diaphragm as claimed in claim 8 wherein the thermosetting resin is a phenol-formaldehyde resin.

References Cited in the file of this patent UNITED STATES PATENTS 1,853,343 Filippo Apr. 12, 1932 2,502,853 Keddie Apr. 4, 1950 FOREIGN PATENTS 863,084 Germany Jan. 15, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION February 17, 1959 Patent No. 2,873,813

William W. Haerther, Jr, et al It is hereby certified that error appears in the -printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 45, for "of" first occurrence, read and column 2, line 37, for opeings read openings column 3, line 28, for curse read cure column 4, line 56, for "acoutic" read acoustic column 5, line 8, for "curring? read curing Signed and sealed this 18th day of August 1959.

(SEAL) Attest:

KARL AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION February 17, 1959 Patent No. 2,873,813

' William W. Haerther, Jr 'et al e -printed specification rror appears in th that the said Letters rtified that e rection and d patent requiring cor s corrected below.

It is hereby ce of the above *numbere Patent should read a Column 1, line 45, for of first occurrence, read and column 2, line 37, for "opeings" read openings column 3, line 28, for curse" read cure column 4, line 56, for "acoutic read acoustic column 5, line 8, for "curring" read curing and sealed this 18th day of August 1959.

Signed (SEAL) Attest: KARL AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Officer 

